1. Field of the Invention
The present invention relates to an engine revolution control apparatus for a vehicle, and more particularly it relates to control of revolutions of an engine when the engine is in the idling state.
2. Description of Related Art
With a conventional engine revolution control apparatus for a vehicle, when an engine is in the idling state, the apparatus sets target revolutions of the engine corresponding to the load of the engine, and then controls an air control valve being provided in a by-pass conduit for by-passing a throttle valve so that actual revolutions of the engine can be converged onto this target number of revolutions. The conventional engine revolution control apparatus for a vehicle controls revolutions of the engine according to both the basic air volume to be set corresponding to the load of the engine and the revolution feedback correction volume to eliminate the deviation between the actual revolutions and the target revolutions. Both of the basic air volume and the target revolutions are calculated according to such factors as deciding the state of operation of the engine.
In addition, the apparatus learns the revolution feedback correction volume so that the actual revolutions can be coincident with the target revolutions. When the state of the engine is shifted from the idling state to the non-idling state and then returned to the idling state, the revolution feedback correction volume which was learned in the former idling state is to be used to learn the revolution feedback correction volume in the latter idling state.
Incidentally, the engine revolution control apparatus for a vehicle controls the air supply volume to the engine by controlling the opening of the air control valve as described above, and the fuel supply volume to engine is decided by this air supply volume to the engine, and then, revolutions of the engine in the idling state is to be controlled.
In the above conventional engine revolution control apparatus for a vehicle, when a component which consumes current and thus affects the engine load, but which does not fetch a detection signal, such as an ON signal of a headlight, is actuated while the engine is in a non-idling state and as soon as the engine is directly returned to idling state, the revolution feedback correction volume which was determined in the idling state not having such a component activated is used to determine the adjustment rate of the air supply volume. In other words, the above case can be seen, for example, when the vehicle stops at a crossing, the engine revolution control apparatus for the vehicle determines the revolution feedback correction volume. Thereafter, when the vehicle is traveling, a current consumer, such as the headlight or a heater, is turned on, and then when the vehicle stops again at another crossing, the revolution feedback correction volume which was determined before is to be used. However, when the engine begins idling again, the air supply volume correponding to the current consumer will be inadequate. Accordingly, the actual revolutions of the engine will temporarily become less than the target revolutions as soon as the engine begins idling, and the engine may stall.
The reduction of the actual revolutions can be corrected and avoided when the next revolution feedback correction volume is determined. However, the next revolution feedback correction volume may not occur for awhile so that the vehicle driver will be discomforted as he or she drives the vehicle.